Peer and lay health work for people experiencing homelessness: A scoping review

Homelessness poses complex health obstacles for individuals and communities. Peer and lay health worker programs aim to increase access to health care and improve health outcomes for PEH by building trust and empowering community-based workers. The scope and breadth of peer and lay health worker programs among PEH has not been synthesized. The primary objective of this scoping review is to understand the context (setting, community, condition or disease) encompassing peer and lay health worker programs within the homelessness sector. The secondary objective is to examine the factors that either facilitate or hinder the effectiveness of peer and lay health worker programs when applied to people experiencing homelessness (PEH). We searched CINHAL, Cochrane, Web of Science Core Collection, PsycINFO, Google Scholar and MEDLINE. We conducted independent and duplicate screening of titles and abstracts, and extracted information from eligible studies including study and intervention characteristics, peer personnel characteristics, outcome measures, and the inhibitors and enablers of effective programs. We discuss how peer and lay health work programs have successfully been implemented in various contexts including substance use, chronic disease management, harm reduction, and mental health among people experiencing homelessness. These programs reported four themes of enablers (shared experiences, trust and rapport, strong knowledge base, and flexibility of role) and five themes of barriers and inhibitors (lack of support and clear scope of role, poor attendance, precarious work and high turnover, safety, and mental well-being and relational boundaries). Organizations seeking to implement these interventions should anticipate and plan around the enablers and barriers to promote program success. Further investigation is needed to understand how peer and lay health work programs are implemented, the mechanisms and processes that drive effective peer and lay health work among PEH, and to establish best practices for these programs.


Background
Homelessness describes the situation of an individual without stable, safe, permanent, appropriate housing, or the means and ability of acquiring it" [1].Homelessness converges with various intersecting identities and forms of marginalization, particularly affecting Indigenous and refugee populations and specific definitions of homelessness have been developed to encompass these diverse considerations [1].Based on current estimates, more than 235,000 people in Canada experience homelessness in any given year, and 25,000 to 35,000 people may be experiencing homelessness on any given night [2,3].In the United States, over 580,000 people may be experiencing homelessness on a single night [4].Homelessness is a growing concern in many countries and can lead to a range of negative health, social and economic outcomes for those affected [5].For example, treatment and prevention of health issues may be neglected due to various barriers such as competing needs for food and shelter, lack of access, stigmatization and discrimination, financial barriers, complex documentation requirements, and limited health literacy [6].
However, the scope and operational enablers and inhibitors of peer and lay health programming among people experiencing homelessness has not been synthesized.We conducted a scoping review to identify evidence relating to peer and lay health worker programs related to people experiencing homelessness to further identify the key characteristics and inhibitors/ enablers of these programs.

Definition of peer and lay workers
Peer and lay support workers, who are individuals without professional training but with a commitment to helping others, can provide support to people experiencing homelessness by offering their expertise, practical assistance and a sense of community."Lay" refers to a community member who has received some training to promote health or to carry out some healthcare service, but is not a health care professional [7]."Peer" refers to a community member who shares similar life experiences to the community with which they work [8].Peer support workers can draw on their lived and living experience to provide support to others experiencing similar situations.Peer support work can be defined by offering and receiving help, based on shared understanding, respect and mutual empowerment between individuals in similar scenarios [8].The use of peer support has been long established in the mental health sector and has recently been implemented in other service areas such as substance use treatment, harm reduction, chronic disease management, homelessness, and sex work [9][10][11].Various terms for lay and peer support worker are used interchangeably in the literature such as, peer health worker, peer specialist, peer advisor, lay support worker, lay health worker, community health worker, community support worker, peer ambassador, health ambassador, among others.[7][8][9][10][11].

Question and objectives
This scoping review aimed to map the extent, range, and nature of literature on the engagement of lay and peer workers in health services for people experiencing homelessness.The participants in this review were people experiencing homelessness (PEH).The concept explored was characteristics of effective peer and lay health worker programs in the homeless sector.In terms of context, the review considered studies that included people experiencing homelessness participating in any type of peer or lay health worker programs.The primary objective of this scoping review was to understand the context (setting, community, condition or disease) encompassing peer and lay health worker programs within the homeless sector.The secondary objective was to examine the factors that either facilitate or hinder the effectiveness of these programs when applied to PEH.

Protocol and registration
The scoping review was conducted based on the JBI methodology for scoping reviews [12] and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) [13].A scoping review protocol was developed and registered with the Open Science Framework (osf.io/u4yp8).

Information sources
A preliminary search of Medline (Ovid), the Cochrane Database of Systematic Reviews and JBI Evidence Synthesis was conducted.A review by Barker and Maguire in 2017 [14] reported on the effectiveness of intentional peer support on young adults and adult homeless persons.That review found 11 articles describing ten studies that examined the focus of intentional peer support with a homeless population; demonstrating limited evidence of intentional peer support with a homeless population [14].This review was conducted prior to the COVID-19 pandemic, and substantial new work in the field has been published in the intervening years [15,16].A second review by Lloyd-Evans and colleagues in 2014 [17] reported the impact of peer support for people with severe mental illness, but did not specifically address the population of people experiencing homelessness.This initial search was validated using a set of ten eligible papers [14,[18][19][20][21][22][23][24][25] to ensure that papers with one or more of the relevant themes were retrieved by our search strategy.
We conducted an electronic search of MEDLINE, CINHAL, Cochrane, Web of Science Core Collection, PsycINFO, and Google Scholar to identify peer-reviewed publications.The search strategy was drafted by the lead author and refined in consultation with peer-reviewers.The final search strategy for MEDLINE can be found in S1 Text.The search strategy, including all identified keywords and index terms, was adapted for each included database and/or information source.The reference list of all articles was screened for additional studies.The listed databases were searched up until 21 February 2023.Eligible studies were limited to the English language.

Selection of sources of evidence
Eligible papers included studies of any kind that described peer or lay health workers engaged in any kind of health or social program serving people experiencing homelessness.Our review adopted Gaetz and colleagues' definitions of homelessness referring to an individual without stable, safe, permanent, appropriate housing, or the means and ability of acquiring it [1].This includes 1. Unsheltered, including those living on the streets or in places not intended for human habitation; 2. Emergency sheltered, including those staying in overnight shelters for people who are homeless and; 3. Provisionally accommodated, referring to those whose accommodation is temporary or lacks security [1].
Literature referring to other more inclusive definitions of homelessness, such as the Indigenous Definition of Homelessness in Canada, were also included in the review.Specifically, Indigenous homelessness is not defined as lacking a structure of habitation, rather it is described and understood through a composite lens of Indigenous worldviews [1].Participants were not limited to a specific age.Studies that included adults, youth and children of all ages that were experiencing homelessness were considered.
The concept explored in this scoping review was the characteristics of effective peer and lay health worker programs in the homeless sector.Studies applying the use of peer and lay health worker programs within the homeless sector were included in this review.We used the term "peer and lay health worker" programs to refer to a wide range of care redistribution strategies that involve the deliberate integration of non-health professionals into the health workforce team, and especially people with lived experience of homelessness or lived experience with the health condition targeted by the given program.A wide range of terms are used to describe these programs, including peer workers, lay workers, community health workers, health volunteers, and health ambassadors, among others [14,20].Eligible studies were not limited by geographic location.
This scoping review considered analytical observational studies including cohort studies, case-control studies and cross-sectional studies.This review also considered descriptive observational study designs including case series, individual case reports and descriptive cross-sectional studies for inclusion.Qualitative studies were considered that focused on data including, but not limited to, designs such as phenomenology, grounded theory, ethnography, qualitative description and action research.
Following deduplication, citations were uploaded to Covidence software [26] and screened by two independent reviewers for assessment against the inclusion criteria for review.The full text of selected citations was assessed in detail against the inclusion.Reasons for exclusion of sources of evidence at full text that did not meet the inclusion criteria were recorded and reported.All disagreements on document selection were resolved through consensus.

Data extraction and synthesis
We developed an online data extraction tool using Microsoft Forms and Microsoft Excel.The data extraction tool provided with the protocol registration was adapted following initial data abstraction efforts to better reflect the nature of the available data and the objectives of this scoping review.Data was extracted by the lead author.Extracted data included details about the participants, concept, context, study methods and key findings relevant to the review questions.For example, the disease/condition; outcome measured; characteristics of peer workers (i.e., age, gender, background); and training provided to the peer worker.
Context of peer and lay health worker programs, enablers and inhibitors/barriers reported in the included documents were recorded.The lead author extracted text verbatim and synthesized the enablers and inhibitors into themes.We then reported on study characteristics and these themes through narratives and tables.

Selection of sources of evidence
A total of 4119 records were identified in CINHAL, Cochrane, Web of Science Core Collection, PsycINFO, Google Scholar, and MEDLINE.Following the removal of duplicates, 2536 records were identified as potentially relevant for this study.Following title and abstract review, 227 records were considered relevant for full-text review.Based on the inclusion and exclusion criteria, 38 documents were included in the scoping review (See Fig 1).

Populations and personnel
All included studies focused on interventions for people experiencing homelessness combined with a specific socio-demographic or clinical need, such as Veterans experiencing homelessness, COVID-19, mental illness, drug or alcohol use, tuberculosis, diabetes, HIV, Hepatitis C, and intimate partner violence [16, 20, 27-30, 43, 47, 48].Peer and lay personnel were referred to using varied language including "peer-led", "peerdelivered," "community health worker," "peer support worker," "peer-driven interventions," "peer recovery coach," "peer-assisted case management," and "peer navigators."The characteristics of the peer worker varied based on the specific program.Almost all peer workers had a lived experience of homelessness, and experience with the condition or population of interest (i.e., type 2 diabetes, mental illness, addiction/substance use, hepatitis C, opioid use, HIV+ status, intimate partner violence, veterans, etc.).

Interventions
Each study incorporated some form of peer support in the intervention.Rosen et al. reported on a mobile vaccination program to promote vaccine uptake using staff with lived experience of homelessness [19].This resulted in increased COVID-19 vaccination uptake for PEH, as data collected through rapid field studies demonstrated that 16% of participants cited their conversation with staff/peer workers as a primary reason for deciding to be vaccinated [19].Davis et al. implemented peer-led diabetes education in a homeless community.They utilized field notes and post-implementation focus groups to determine that the intervention resulted in increased empowerment and knowledge of signs, symptoms, complications of diabetes, and diabetes medications [29].Croft et al. implemented peer-delivered permanent supportive housing for individuals who were experiencing homelessness and issues with mental health/ addiction [47].In-depth semi-structured interventions were recorded, transcribed and analyzed using a grounded theory approach to determine that the intervention resulted in a decrease in psychological distress (i.e., decrease in number of emergency room psychiatric visits) [47].Four studies implemented a peer-driven intervention for PEH who inject drugs and are HIV positive or hepatitis C positive.These resulted in increases in testing and medication adherence [38,43,48,51].Five studies utilized peer mentors who implemented support groups, one-on-one support, group recreational activities and provided encouragement/advice to homeless youth [22,33,[44][45][46].This supported participant engagement, enhanced health behaviours, improved mental well-being, decreased loneliness, expanded social networks, increased coping skills, enhanced self-efficacy, and diminished use of alcohol and drugs [22,33,[44][45][46].Moledina et al. reported that their peer support programs demonstrated no impact on housing relative to usual care; and no economic evidence was found for peer support [36].Moledina et al. suggests that peer support cannot serve as a stand-alone intervention to promote stability [36].

Enablers and inhibitors of peer and lay health worker programs for PEH
These programs reported four themes of enablers (shared experiences, trust and rapport, strong knowledge base, and flexibility of role) and five themes of barriers and inhibitors (lack of support and clear scope of role, poor attendance, precarious work and high turnover, safety, and mental well-being and relational boundaries).See Table 2 for a summary of enablers and inhibitors of peer and lay health worker programs among PEH.

Enablers
Shared experiences (n = 20).The included studies show that due to their shared experiences, the peer support worker and program participants were able to have mutual understanding of one another and display empathy [14].Shared experience appears to help clients to disclose their needs, and positions peers as facilitators [20,50].Due to their shared experiences, peers view clients as equals and reduce hierarchy in the process of accessing and receiving care [14].In many studies, it was reported that peer support workers were able to motivate and engage clients who were previously unengaged in the program/treatment [32,55].In certain settings such as substance use and addiction, seeing recovery work for the peer made the possibility of recovery more tangible and achievable, and increased motivation for the participant's process of recovery [39].Additionally, a non-judgmental approach and the foundation of trust helped to foster a safer emotional and physical space for interventions to take place [56].Specifically, the relatability and decreased perceptions of stigma aided in this process [39].For example, Salem et al. discussed how participants felt their disease (tuberculosis) was stigmatized, which influenced how they accepted treatment, and that peer workers helped to mediate and reduce that experience of stigma [39].
Trust and rapport (n = 21).A common theme in the included studies was the value of trust and reliability of the peer support worker, both with patients or clients and with other members of the health care or social support team [36].This positions the peer worker to function as a bridge between people experiencing homelessness and program staff, and facilitate Heavy caseload, lack of support from outside services, and long wait lists for programs.

Croft et al., 2013
Peers as a patient advocate; supporting socially excluded patients through sharing their personal experience; gain trust.Cost-effective resource.
Peers have a unique insight into the social dimensions of tuberculosis.
Not reported.

David et al., 2015
Ability to motivate and engage clients who were previously unengaged in treatment.
Ability to build trust with their clients at each client's pace, able to relate to shared experiences, and reducing stigma of diagnoses.
Tension among peer mentors and clients who had shared "street" histories including conflicts over romantic relationships.Barriers to treatment such as transportation and shelter.

Davis, et al., 2016
Strong attendance and participation.Good relationship building skills and ability to provide a sense of empowerment.
Peers having a strong knowledge base of diabetes information.
The complexity of the educational material.Language and speech barriers between peers and clients.

Deering et al., 2009
Small group size allowed for increased cohesiveness and closer bond among members.
Large groups got split up, inhibiting the continuity and closeness and trust that women developed.

Erangey et al., 2020a
Mutual understanding and empathy, reducing stigma, increasing hope for recovery and creating a supportive environment.
Previous trauma, no desire/not ready to engage with program or change and non-supportive environments.

Erangey et al., 2020b
Peers being a familiar face, available, trustworthy and having a nonjudgmental attitude.Peers having shared experiences and ability to model recovery.Mutual aid between peers and clients.Flexibility of work and the peer role.
Dismissed by other service providers; power imbalances.Hard for others to identify them as peer support specialist Lack of attendance from youth.Stigma or objectification.
Having to clarify the peer role to clients who want a friendship.
(Continued ) Disruptive behaviour of clients.

Herts et al., 2020
Ability of peers to form therapeutic relationships with their clients.Able to foster trust and companionship.Flexibility and accessibility.
Lack of adequate supervision and support.High turnover among supervisors Lack of affordable housing options and supports available for clients.

Kidd et al., 2019
Peers' ability to be versatile and create a comfortable environment.Peers' advocacy for clients.Peers being good listener and their proximity to the youth in age and life experience.
Role confusion (i.e., participants struggled with defining the role of the peers initially).Informal drop-in structures of engagement were difficult to plan, deliver, and were poorly attended.

MacLellan et al., 2017
The building of rapport and self-disclosure of shared experiences.Use of respect, reciprocity and friendship; good communication skills; showing acceptance of who the client is; mutual respect and the desire to work together.When HCP staff understand the role of the PA, they work well together because the PA saves them time.
Being professional and non-judgmental.
PAs are often still vulnerable to the context within which they are now working (i.e., one PA could not work with clients in certain parts of the city due to his own recent challenging experiences there).Potential exposure to triggers.Lack of boundaries between PA and clients.

Magwood et al., 2019
Ability of peers to provide physical and emotional safety (i.e., women's only programs).A sense of empowerment, continuity and trust.
Patronizing attitudes and lack of commitment from workers.Loss of autonomy.

Miler et al., 2020
Leadership skill.Creating a sense of community and connection.Peer interventions can also benefit the peer workers themselves and lead to changes in their own behaviour.Able to build a special type of rapport and trust based on shared experience and lack of judgment.
Risk that peer support for people with history of substance abuse could lead to relapse.The need to establish boundaries between peers and clients.Problems with stigma and discrimination.Peers feeling undervalued in their work; lack of clarity regarding the peer role; limited opportunities for career growth.

Moledina et al., 2021
Ability to establish relationships based on trust due to their shared experiences.
Potential harms to peer workers: depression and anxiety symptoms.

Morris et al., 2020
Reduced barriers to testing and treatment.Effective communication skills.Collaboration with the multidisciplinary team.
Not reported.

Nyamathi et al., 2021a
Able to provide a comprehensive continuum of care approach.
Caring peers; ability to offer compassion, support and dedication.
Not reported.

Nyamathi et al., 2021b
Ability to provide emotional support; ensuring confidentiality and trust.Ability to share similar lived experiences.
Being an advocate for clients (being a spokesperson, translator, or accompanying PEH where they need to go).

Difficulty locating clients.
Stigmatization.Food insecurity and lack of transportation jeopardize treatment initiation and completion.

Parkes et al., 2022
The shared lived experience aided in enabling trusting, authentic and meaningful relationships to be developed.The flexible role enabled peer navigators to work beyond the service they were based in.
Flexibility of roles sometimes contributed to tensions between existing staff and the peer navigators.

Ponce et al., 2014
Creating safe emotional and physical spaces; non-judgemental approach.
Having peer workers trained in understanding and addressing trauma.Accessibility-offering multiple meeting sites.
Participants unwilling or unable to engage in services for reasons related to their experiences with their violent/predatory partners.Women reported that their partners did not want them to interact with male staff; fear of judgement; participants having a violent, coercive, or predatory partner.

Resnik et al., 2017
Ability to relate to similar life experiences and build trust.Ability to facilitate connection to services (housing, free telephone, clothing and bus tokens).
Good training provided to peers prior to start of program.
Peers' lack of knowledge (i.e., some Veterans thought that they understood less than they did about how to navigate services).
Clients not being open or receptive to services.

Rosen et al., 2023
Ability to share personal stories and relate to mutual life experiences.Having peers provide harm reduction supplies, food and hygiene kits.
Frequent encampment sweeps fostered government mistrust and made clients resist peer engagement and vaccine delivery.
(Continued ) successful program design and successful client engagement with the program [48].Peers were often trusted by clients as they knew the best language to discuss various health topics, and they were respected by the clients due to their shared experience/similar background [16].
Strong knowledge base (n = 11).The ability to reduce barriers to care and being knowledgeable of the disease/condition (i.e., diabetes, tuberculosis, etc.) was an important enabler of effective lay and peer worker programs [29,39].Peers acted as an advocate for clients to help address other factors that were impacting their health, as they had specific experiential knowledge of the condition that other providers did not [47].For example, peer support workers were able to extend support by utilizing various resources such as mental health, substance use, housing support, medical interventions, and treatment resources [28,40,41].Specifically, they were able to improve linkage to treatment by offering an acceptable, destigmatizing and flexible approach which addressed common barriers faced by low-income, minority individuals [41].
Flexibility of role (n = 5).Flexibility of the role enabled peers to work beyond the service where they were based [52].There are few restrictions to how peers spend their time with clients, therefore, they can tailor their approach specific to each individual client [35].For example, peer support workers do not have to work from a specific location-they often engage with clients at locations of their choosing to increase accessibility to the program [35].Peers were able to provide support to individuals at any given time based on their needs.This highlighted the importance of flexible and person-centered support for individuals that are severely and multiply disadvantaged [52].Specifically, this follows the PIE approach, which refers to psychologically informed environments [52].This involves developing psychological awareness of individual's needs; valuing training/support for staff; creating effective/safe service environments; and, focuses on the roles and responsiveness of the services to focus on improving relationships [52].An additional benefit of role flexibility is that it allows peers to develop various skills which may present them the opportunity to re-enter the workforce for those who previously struggled with fixed employment [18].

Inhibitors/barriers
Lack of support and clear scope of role (n = 9).A recurrent inhibitor identified was the heavy caseload, lack of support from outside services and long wait lists for the programs [28].With the limited number of peer workers engaged in most programs, it was difficult for them to fully engage with the high volume of participants interested in the programs.The multidisciplinary team occasionally found it difficult to identify the peer support workers as a member of the care team.As a result, peer workers reported being treated in a dismissive manner by other service providers [33].Role confusion was cited as an inhibitor as service providers and participants struggled with defining the role of the peers [44].For example, the specific roles of peers in the early months of the intervention were less clear than was the case for other health care providers [44].Role confusion contributed to tensions and conflicts between existing staff and the peer support workers [52,55].
Poor attendance (n = 7).Lack of consistent engagement from peer and lay workers and irregular attendance from program participants (PEH) was identified as an inhibitor to program success [42,46,56].Continuity of program staff was imperative to maintaining rapport and trust among the participants.On the other hand, program participants (PEH) did not have regular attendance for various reasons (i.e., unstable living conditions, transportation barriers, substance use, lack of readiness to fully engage in program, etc.), which hindered positive program outcomes [39,41,45,46,53].
Precarious work and high turnover (n = 7).Several reports noted high turnover of peer workers [28,35,42].Reasons for high turnover may be due to precarious work opportunities, lack of job security, low pay, heavy workload, feeling undervalued, poor job-progression opportunities and inadequate sick leave [16,18,55,57].Many peer support positions are temporary, contract-based, or grant-funded, which creates a constant sense of job insecurity.Additionally, the heavy workload may lead peer workers to feel overwhelmed and undervalued, leading to burnout and a desire to leave their positions.
Safety (n = 4).Safety of peer support workers while actively engaged in the role was cited as a common inhibitor.Various programs utilized incentives for treatment and testing, and peer support workers would be responsible for carrying gift cards, cash, etc. which positioned them as targets for theft [16].Some peer support workers had prior conflicts with the community they were serving, such as violent encounters and conflict over intimate relationships, which introduced safety concerns while performing job duties [16,32].
Mental well-being and relational boundaries (n = 9).Various studies reported peers had difficulty maintaining professional boundaries with clients, while still being supportive [14,48,50,54,57].Challenges with personal boundaries would occasionally occur where peers developed friendships, lent money, borrowed items, etc. [49,50].To maintain a therapeutic relationship, peers would face the delicate task of clarify their role to clients without eliciting shame or rejection, especially when clients were seeking a friendship or more personal relationship [33].On the other hand, peers would clarify that their roles were also not the same as professional clinicians either, and that professional approaches to boundaries could not be transposed into peer or lay work, especially as they shared similar lived experiences as their clients.Peers who had a history of substance abuse and were working to support clients with substance use concerns reported a risk of relapse [18,57].Some studies reported that peer work had the potential to negatively impact peers' mental health, including worsening symptoms of depression and anxiety [36,46].

Discussion
This scoping review identified 38 sources of evidence describing enablers and inhibitors to peer and lay health work programs in the homeless sector published between 1995 and 2023.The majority of the studies were published after 2017, which indicates new research is rapidly emerging on this topic.
The included programs were effective when they were able to build trusting relationships with staff and clients and reduce the barriers that PEH faced when accessing programs.Peers having an intimate knowledge of homelessness and shared lived experiences regarding the condition/disease of interest, led to the ability to connect and build strong rapport [14].In terms of programs related to substance use/recovery, peers had mutual understanding and empathy, were able to reduce stigma, and increase hope for recovery by creating supportive environments for clients [22].Rather than clients having to travel to program locations, peers were able to improve accessibility by meeting clients at locations they chose (i.e., the homeless shelter, coffee shops, parks, etc.) [35].
A critical element of effective peer and lay health support programs is the concept of mutual benefit: both peers and clients benefit from utilizing these programs.Peer support work programs provide mutual benefit to both peer workers and clients because they create a sense of empathy and understanding between them.By working together, they have the capacity to form supportive communities that help clients build resilience, reduce isolation, and improve their overall mental and physical health.Additionally, clients benefit from the expertise and knowledge from peer workers, who provide them with practical strategies to manage their health and help them navigate the healthcare system.Peer support work programs provide a sense of purpose and fulfillment for peer workers, who can use their own experiences to help others while gaining valuable training and skill development.Throughout this process, peer support workers also gain employment references and opportunities for other work opportunities which in turn, may help bring them out of homelessness [14].
Peer programs create a safe and inclusive emotional and physical environment where participants can talk freely about their shared lived experiences.Peer support work programs are beneficial to individuals experiencing homelessness in numerous ways such as providing emotional support, encouragement, and motivation.These programs also offer practical assistance, such as food, shelter, healthcare services, and housing and employment assistance to provide support to PEH.Peer support work programs empower individuals to take responsibility for their own lives by building resilience, confidence, and taking control of their health.They provide a platform where individuals can share their experiences and success stories, which can significantly contribute to the overall process of ending homelessness through a multidisciplinary and collaborative approach.

Limitations
This scoping review has limitations.First, while two reviewers independently undertook the screening and document selection process, only the lead author undertook the data extraction and charting process.However, we do not believe that this compromises the rigor of this review due to the nature of the evidence selected.Secondly, the quality of included documents/studies were not assessed, therefore, recommendations cannot be given based on the quality of the selected evidence.A final limitation of this scoping review was restricting the search to include only articles written in English, as the inclusion of other languages may have potentially resulted in useful information and perspectives on the topic.

Conclusion
This review demonstrates that peer and lay health programs been successfully implemented to serve people experiencing homelessness.Overall, peer and lay health work programs are effective for people experiencing homelessness in various contexts (i.e., substance use, chronic disease management, harm reduction, mental health, etc.).These programs may experience challenges due to the many barriers that PEH experience when trying to access and maintain participation in services.Many programs were also able to report facilitating factors that were able to overcome these inhibitors and implement successful peer and lay support programs.Further investigation is needed to understand how peer and lay support work programs are successfully implemented within the homeless population in different contexts (i.e., substance use, transitional housing, mental health, etc.) and to build best practice recommendations for these programs.Organizations seeking to implement these interventions should anticipate and plan around known facilitators and barriers to promote success of the program.

Table 2 . Summary of enablers and inhibitors of peer and lay health worker programs among PEH.
Choi et al., 2022Peer ambassadors (PAs) address issues of access and mistrust through preexisting rapport and trust; knew the best language to use to discuss vaccines; were respected by their neighbours.Strong interpersonal skills (calm, kind, non-judgmental and confident).Community health workers (CHWs) saw potential for longer-term employment of program participants as PAs or even eventually as CHWs; connecting PAs with job opportunities and skills trainings.

Table 2 .
(Continued)Flexibility of peer work can present an opportunity to re-enter the labour market for a group that may struggle with fixed employment.Acceptance of efforts to include the peer support workers as part of the team (i.e., inclusive approach).Non-judgmental communication and trust gained by sharing their lived experience; ability to remove barriers to care.Volunteer role is characterized by instability and insecurity.Barriers of power in the 'peer' relationship.Risk of relapse for the peer.As peers take on more advanced roles previously carried out by other health professionals, this can lead to conflict if not clearly defined. https://doi.org/10.1371/journal.pgph.0003332.t002